Magnets have been used for a long time in a variety of applications, including the use of permanent magnets to attract and hold ferro-magnetic objects, to clamp objects and assemblies during manufacturing. In some circumstances, permanent magnets may constitute the only practical way of clamping objects in confined spaces during the manufacturing process. In addition to these permanent magnets, larger electromagnetic clamps and chucks also find extensive application in the manufacturing industries.
Both permanent magnets and electromagnets have significant limitations, although they are useful in a wide variety of applications. Electromagnets pose a hazard due to the very high currents and voltages that are required to generate magnetic fields of sufficient strength to be useful in industrial applications. Moreover, due to their bulk and necessary electrical power leads, electromagnets are frequently not well suited for use in confined areas. On the other hand, permanent magnets generally have a limited clamping force due to their low strength magnetic fields. In addition, their magnetic fields cannot be shut off, or easily redirected in a portable device. Usually, large magnetic forces are necessary to shut off a magnetic clamp of permanent magnets, by rotating the permanent magnet away from the workpiece being clamped.